The present invention, generally, relates to a new and improved system for the ordering of computed ranges along a simulated radar sweepline between the beginning and the intersections of boundaries of polygonal shapes describing significant ground features. More particularly, the invention permits unambiguous interpretation of a variable length list of intersection ranges obtained by computing the ground range from the simulated radar transmitter to the boundary of each feature intersected by the sweepline, regardless of shape, orientation and convexity.
Electronic data processing systems and equipment have a wide and important function in today's business, research and scientific activities. The electronic equipment and other machines used in such data processing systems usually have a considerable amount of data supplied to them.
Generally, the data processing systems used in business activities, such as maintaining continuous balances in banks and maintaining inventory systems, involve large amounts of data and other information and relatively few simple computational operations. While data processing systems used for research or scientific purposes involve a large number of complex computational operations and a relatively small amount of general information, there are, of course, many exceptions to these generalities.
The data used in such systems is often coded in a manner exemplified by various types of binary codes. For example, binary bits may be used to identify characters such as Arabic numerals, letters of the alphabet or other symbols. These characters may be combined to form records of any convenient length.
Records formed from binary characters may be placed on any of the well-known means of storing, such as punched tape, magnetic tape, punch cards, or magnetic drums, for providing the medium of information in data processing systems. Information supplied to the input which is stored within or appears at the output of these systems is often in a random order with reference to that which is desired.
Therefore, it is common for data processing systems to include means for arranging the records containing information into a desired sequence. Only a portion of a record, known as the "control field", is utilized in determining the precedent of one record over another in a particular sequence.
There are several well-known types of sorting systems used in present day commercial data processing systems. For example, when the record medium is punched cards, a method known as pigeon-hole sorting may be utilized. Such a file of cards is sorted into pockets according to the least significant digit of the control field of each card.
Another known system of sorting information is magnetic tape merging. According to this system, a file of records on magnetic tape is separated into two tape units. The initial records of these two tapes are fed into a storage device.
The system of magnetic tape merging is subject to several disadvantages, however. Most important of these is that a considerable amount of equipment is required in order that the comparison steps take place.
Recently, other uses for sorting have arisen which require higher speed; for example, many real-time processes exist in which sorting of items is required. Among these real-time processes are simulations of physical models to study, duplicate, control and/or otherwise utilize the real world counterparts.
One such use is flight simulation, in which the physical models simulated are those representing the various sensory interfaces between a flight crewman and his immediate environment. The most demanding of these models are those which produce simulated visual imagery, either to duplicate sight directly (computer image generation) or to duplicate imagery produced by non-human sensors, such as infra-red sensors, television or radar.
The features with which the invention is concerned represent significant geographic areas collected into a radar landmass data base describing a simulated environment for use in a digital radar landmass simulator. A digital radar landmass simulator is an air crew training device which presents a digitally-generated radar display simulation for use in conjunction with flight training.
For the purposes of this description, the sweepline on a simulated radar visual display screen is assumed to extend indefinitely and the features are assumed to be of limited extent. Therefore, the list of intersection ranges will always contain an even number, with half representing "entrances" and the other half representing "exits" from any given feature area. This is a readily demonstrated attribute of any straight line intersecting any closed area.
However, the initial list can be in a mixed-up order, depending on the order in which the feature boundary coordinates are given to the intersection processing logic circuit. This depends, further, on the arbitrary choice of absolute feature origin on the sweepline, shape of the feature and orientation relative to the particular sweepline being generated.
It is sufficient for the purpose of this description that each intersection has been detected and the correct range has been computed to a specified accuracy, and by establishing a boundary description convention, each intersection has been identified readily as either entrance or exit. The boundary description convention should stipulate, for example, that each boundary segment is a vector proceeding counterclockwise around the feature area (shown in FIG. 4).
Hence, the inside of the feature would lie to the left of each boundary segment. A segment crossing the sweepline from left to right would result then in an entrance intersection, and a segment crossing from right to left would result in an exit intersection.
The information as to whether a computed intersection with a feature boundary is an entrance or an exit can be added as a single binary bit flag (binary "one" representing "entrance"; binary "zero" representing "exit") to the range value in the intersection list for each feature. Other feature or intersection parameters (such as reflectance code, height, boundary aspect, etc.) also can be added to each feature description, as required.
The purpose of the invention is to reduce this variable length list to a corresponding group of intersection pairs, each pair representing one crossing of the sweepline over part of the feature area. Once this is done, the sweepline radar profile is obtained readily by applying the individual feature descriptions to the corresponding sweepline range segment described by the paired intersections. Also any ambiguity resulting from data base anomalies or range computation inaccuracies is resolved during the pairing or ordering process.